1. Field of Invention
This invention relates generally to a light projector adapted to create a light show on a remote surface serving as a display screen, and more particularly to a hand-held light projector which when shaken by an operator produces on the screen Lissajous figures in varying patterns and in a selected color, thereby creating a light show whose nature depends on how the projector is shaken by the operator.
2. Status of Prior Art
In a cathode-ray oscilloscope, an electron beam is projected through vertical and horizontal deflection plates onto a phosphorescent screen to produce a light trace whose path is the resultant of the right-angle vertical and horizontal deflection forces.
A cathode-ray (C-R) oscilloscope is useable as a frequency comparison instrument to determine the frequency of an unknown wave by visually comparing it with a wave of known frequency. If the horizontal and vertical coordinates of a point are each given by a a sinusoidal wave function of time, the path traced by this point is no longer a sine wave, but varies with the relative time phase of the sine waves and with their relative frequencies.
Thus if the two waves have the same frequency and are in time phase or are 180 degrees out of phase, then the resultant trace on the C-R screen a straight line. But for all other values of phase displacement, the trace creates an ellipse which becomes a circle when the waves have equal amplitudes and are 90 degrees displaced in phase. When the frequencies of the two waves are not the same, the resultant pattern is more complicated, and may have a figure of eight or a more complex shape. These shapes or patterns are known in the oscilloscope art as Lissajous figures.
A light projector in accordance with the invention, makes no use of an electron beam as in a C-R tube, but provides an analogous operation in which a light beam is deflected concurrently in the horizontal and vertical directions to create Lissajous figures on a remote display screen. In practice, this screen may be an ordinary wall in a room.
A light projector in accordance with the invention may make use of an ordinary incandescent bulb whose light rays must be focused to produce a light beam coming to a point on the display screen to trace a light pattern thereon.
Alternatively, use may be made for the same purpose of a laser beam projector such as that disclosed in the Kimble et al. U.S. Pat. No. 4,102,059 in which a coherent light beam is generated and therefore requires no focusing to come to a point. However, a laser beam light projector in accordance with the invention, though it includes no focusing lens, is more costly than a projector using an incandescent bulb.